Significance

Periodic episodes of massive iceberg discharges from the large Northern Hemispheric ice sheets into the North Atlantic Ocean occurred throughout the last glacial cycle. It is still not clear whether they resulted from internal ice dynamics alone or were possibly externally driven. Results of our simulations of the Laurentide Ice Sheet forced by oceanic circulation changes support the hypothesis that these ice discharges were induced by the collapse of a buttressing ice shelf and the subsequent acceleration of inland ice streams. This provides a new basis for understanding the dynamics of the coupled cryosphere–climate system of glacial cycles. Additionally, it has strong implications for the stability of the marine parts of the Antarctic ice sheet given anthropogenic oceanic warming.

Abstract

Proxy data reveal the existence of episodes of increased deposition of ice-rafted detritus in the North Atlantic Ocean during the last glacial period interpreted as massive iceberg discharges from the Laurentide Ice Sheet. Although these have long been attributed to self-sustained ice sheet oscillations, growing evidence of the crucial role that the ocean plays both for past and future behavior of the cryosphere suggests a climatic control of these ice surges. Here, we present simulations of the last glacial period carried out with a hybrid ice sheet–ice shelf model forced by an oceanic warming index derived from proxy data that accounts for the impact of past ocean circulation changes on ocean temperatures. The model generates a time series of iceberg discharge that closely agrees with ice-rafted debris records over the past 80 ka, indicating that oceanic circulation variations were responsible for the enigmatic ice purges of the last ice age.

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